Carbamate-functional materials have found particular utility in coating compositions as crosslinkable resins. Curable coating compositions utilizing carbamate-functional resins are described, for example, in U.S. Pat. Nos. 5,693,724, 5,693,723, 5,639,828, 5,512,639, 5,508,379, 5,451,656, 5,356,669, 5,336,566, and 5,532,061, each of which is incorporated herein by reference. These coating compositions can provide significant advantages over other coating compositions, such as hydroxy-functional acrylic/melamine coating compositions. For example, the coatings produced using carbamate-functional resins typically have excellent resistance to environmental etch (also called acid etch) and degradation. Environmental etch results in spots or marks on or in the coating that often cannot be rubbed out.
Automotive finishes are applied in a series of coating layers, with each coating layer providing an important function in the performance of the composite finish. For instance, primer coating layers are used to protect the substrate from corrosion, chipping, and delamination of the coating from the substrate. Surfacer and primer surfacer layers are commonly used to provide a smooth surface upon which to apply the topcoat layers, and may add increased corrosion protection or chip protection. The topcoat layers provide beauty as well as protection against scratching, marring, and environmentally-induced degradation. Topcoats for automotive and other industrial applications may be a one-layer coating, in which the color is generally uniform through the coating layer, or a clearcoat-basecoat composite coating, having a colored basecoat layer underlying a transparent clearcoat layer. Basecoat-clearcoat composite coatings are widely used and are notable for desirable gloss, depth of color, distinctness of image and/or special metallic effects. Composite coatings are particularly utilized by the automotive industry to achieve a mirror-like, glossy finish.
Green, U.S. Pat. Nos. 5,872,195, 5,852,136, 5,693,724, and 5,693,723, describe carbamate-functional components prepared by reacting an epoxide-functional compound with a carboxylic acid-functional compound to produce a reaction product having hydroxyl functionality, then reacting the hydroxyl functionality with cyanic acid, which may be formed by the thermal decomposition of urea, or a carbamate compound having functionality reactive with the hydroxyl functionality, e.g. by esterification.
One method of producing carbamate-functional materials is by transcarbamylation or transesterification reaction of the hydroxyl-functional material with an alkyl carbamate (e.g., methyl carbamate, ethyl carbamate, or butyl carbamate). The reaction is carried out using a catalyst, such as an organometallic catalyst (e.g., dibutyl tin dilaurate). This method has certain drawbacks, one of which is that the presence of acid poisons the tin catalyst. If the carbamate material is produced by transcarbamylation and acid functionality is desired, then it is necessary to introduce the acid functionality after the transcarbamylation is complete. Another drawback is that the transcarbamylation process can require certain additional, expensive equipment to handle the low molecular weight carbamate compounds that are typically used in the process.
It would be desirable to produce carbamate functional materials such as carbamate functional polymers by a method that avoids the difficulties of the transcarbamylation process.